Development of the hottest overhead camshaft

Development of overhead camshaft

automotive engine is composed of crank connecting rod mechanism, valve train, cooling system, fuel system, lubrication system, electrical system and body, etc. there are nearly a thousand large and small parts, among which the camshaft is the most representative. In the technical specification table of modern cars, the term "camshaft" can often be seen in the column of engine performance

camshaft belongs to the valve mechanism of the engine. If the valve mechanism is guaranteed, it needs to be equipped with a regulated power supply certificate. The engine regularly fills the fresh combustible mixture into the cylinder during operation, and timely discharges the burned exhaust gas out of the cylinder. It is composed of inlet valve, exhaust valve, valve tappet, tappet, rocker arm, camshaft, etc. the camshaft is also called peach shaft or eccentric shaft because its cross-sectional shape is similar to a peach. It is the driving part in the valve mechanism, which specially drives the valve to prepare clean samples to open and close on time. The camshaft structure of various models of engines is similar, and the main difference lies in the installation position. The number, shape and size of cams are different, especially the installation position of camshaft, which is listed as an important symbol to distinguish engine structure and performance. At present, the cam installation position of the engine is divided into three forms: lower, middle and top

due to the fast speed of the car engine, the speed per minute can reach more than 5000 rpm. In order to ensure the intake and exhaust efficiency, the intake valve and exhaust valve are hung upside down, that is, the overhead valve device, which is suitable for three installation forms of camshaft. However, if the lower or middle camshaft is used, because the distance between the valve and the camshaft is far, and the auxiliary parts such as valve tappets and tappets are required, there are many valve transmission parts, the structure is complex, the engine is large, and it is easy to produce noise under high-speed operation. However, using the overhead camshaft can change this phenomenon. Therefore, modern car engines generally adopt overhead camshafts, which are arranged on the top of the nearest engine, shortening the distance between the camshaft and the valve, omitting the tappet and tappet of the valve, simplifying the transmission mechanism between the camshaft and the valve, and making the structure of the engine more compact. More importantly, this installation method can reduce the reciprocating quality of the whole system and improve the transmission efficiency

of course, everything has its two sides. On the one hand, the overhead camshaft shortens the distance from the valve, on the other hand, it widens the distance between the camshaft and the crankshaft. Because the camshaft is driven by the crankshaft, the chain and sprocket must be used to rotate as soon as the distance between them is extended. The structure is much more complex than the gear meshing transmission of the lower camshaft. Nevertheless, people prefer to use overhead camshaft to weigh the advantages and disadvantages

now it has high alignment accuracy. The overhead camshaft has many forms of driving valves, including rocker transition drive and direct drive. Among them, the direct drive has relatively low requirements for the design of camshaft and valve spring, and the inertia of reciprocating motion is the least, which is especially suitable for high-speed car engines. In addition, in recent years, toothed belts are widely used in high-speed car engines to replace the transmission chain. This kind of belt is made of neoprene and mixed with glass fiber and nylon fabric to increase strength. Using toothed belt instead of transmission chain can reduce noise, reduce structural quality and reduce cost

car engines are divided into single overhead camshaft (SOHC) and double overhead camshaft (DOHC) according to the number of overhead camshafts. Because the medium and high-end car engines are generally arranged with multi valve and V-shaped cylinders, it is necessary to use double camshaft to control the intake and exhaust valves respectively, so the double overhead camshaft is adopted by many famous brand engines. As the installation method of camshaft directly relates to the structure and performance of the whole engine, the overhead camshaft, like multi valve, is also regarded as an important symbol to measure the car engine and is listed in the car technical specification table. (end)